Blend flour, sugar, baking poser, salt and instant coffee in a bowl. Add buttermilk, vanilla, butter and walnuts. Mix very well so that batter is very firm.
Spread in your prepared pan and pour Coffee Caramel Sauce on top.
Bake until bubbles have risen to the top and it feels firm to the touch, about 45 minutes.
Transfer to rack and cool.
Cut and serve warm with whipped cream or ice cream.